The interaction between lymphoma (RCS) and host CD4+ T cells in SJL mice, and the properties of SJL lymphomas that make these tumor cells stimulatory for syngeneic T cells, will be examined. The cytokines required for growth of RCS cell lies will be further defined and the relationship between those produced by host T cells and any possible autocrine factors of RCS cells examined. The Vbeta of the TCR on RCS-specific hybridomas will be characterized. The reason for the superantigen-like behavior of RCS will be sought and the nature of the peptide associated with the I-A of the tumor will be investigated. Multiple immunoglobulin gene rearrangements have been found in the in vitro cell lines derived from RCS. We will examine how early in the process of lymphoma formation these abnormalities, which appear to be due to the deletions in the switch regions, occur by examining in vitro and transplantable cell lines developed from early primary lymphomas. If, like the first in vitro cell line (cRCS-4) that we developed that way, more of such cell lines prove to exhibit surface IgA, the relationship between serum paraprotein idiotype and sIg will be reexamined.